The invention relates to an electromagnetic relay with moving contacts which are operated by an armature and cooperate with fixed contacts.
Practically all kinds of electromagnetic relays are constructed in such a way that an armature in the form of a pivoting armature, rotating armature or the like, is operated electromagnetically, thereby causing displacement of contacts which, for example, disengage or engage corresponding fixed contacts. Moving contacts as well as fixed contacts are usually mounted on contact springs. To this end, moving contacts can be operated by operating bridges or the like which are influenced by the armature.
Opening the contacts in all such relays, particularly those adapted for switching high power, results in an arc as a result of which the contact surfaces are destroyed. Such a destruction of the contacts also substantially reduces the service life of the relays because, on the one hand, contacts with a destroyed surface no longer reliably provide an adequately low transfer or contact resistance and, on the other hand, contact burning also influences all the other operating values of the relay to a substantial extent. For example, the contact pressure of burned contacts is reduced. Moreover, the springs of burnt contacts store less energy so that the armature motion which is effected or influenced by the spring force is slowed down and, depending on the construction, causes slower contact opening speeds and accordingly increased contact burning or involves other disadvantages.
Arcing between opening contacts of a relay rapidly renders such a relay useless, particularly if the spark gap is maintained for a prolonged period and carries a heavy current. Contact burning of this kind can be retarded to a certain extent by using high-grade contact material. There are naturally limits to this procedure, so that the service life of a relay and its reliability depends in the first place on the extent to which it is possible to avoid prolonged, severe arcing between opening contacts. Advantages in this and other respects are obtained by encapsulating the entire relay or at least the contacts in a protective atmosphere, but this procedure is costly and therefore not always possible.